A vacuum brake force booster of this type is generally disclosed in EP 119 880 A1. Principally, it must be taken into consideration that the interior of a vacuum brake force booster houses two pneumatic chambers which are separated from each other by a movable wall and are evacuated in the non-actuated condition of the brake system. Beside mechanical stresses of most different types, the housing must transmit pressure forces due to the differential pressure between the residual pressure in the interior of the brake force booster and the external atmospheric pressure so that there is an imperative need for defined minimum wall thicknesses of the housing which is made up of two wall elements fastened to one another. In terms of weight reduction of all components installed in an automotive vehicle, there is the increasing trend of employing, as a material, materials with a low specific weight, such as aluminum or plastics, or of using steels of higher rates of strength. In addition, a permanent objective is to minimize the wall thickness of component parts. Therefore, it has been known in the art, see e.g. the above-mentioned patent application, to provide reinforcing elements which extend through the interior of a brake force booster housing and have a thin-walled tubular shape. On the one hand, this means ensures that the two wall elements remain at a defined distance from each other even with a small wall thickness and with high pressure forces, so that the housing of the brake force booster will not yield. On the other hand, a tubular reinforcing element permits passing a fixing anchor through the interior of the brake force booster and attaching the brake force booster along with a master brake cylinder to a wall of an automotive vehicle.
An arrangement of this type suffers from the disadvantage that the slots and gaps which are produced by the use of the tubular reinforcing element must be sealed pressure-tightly. This applies, on the one hand, to slots in the wall elements which extend from the interior of the brake force booster in an outward direction and, on the other hand, also to slots between the two pneumatic chambers.
In the above-mentioned patent application, the reinforcing element is arranged in a third chamber which is separated by the two pneumatic chambers by means of an additional sealing element. Such a measure produces a major cost increase in large-series production which is a significant disadvantage. Besides, the mentioned third chamber is quasi permanently subjected to atmospheric pressure so that its surface does not assist in the generation of the boosting force. This shortcoming is principally unacceptable in view of ever more reduced mounting spaces and the necessity of still more powerful automotive vehicle brake devices.
An object of the present invention is to provide an optimally sealed vacuum brake force booster which does not only permit low-cost manufacture in large quantities but also satisfies the demands with respect to structural volume, weight, strength and capacity. One objective of special emphasis is to configure the assembly made up of brake force booster and master brake cylinder so that it can be installed easily into an automotive vehicle.
This object is achieved by the present invention wherein the reinforcing element on at least one end passes over into a radially extending fastening portion which extends at least in a partial zone in parallel to the associated wall element and is supported on the wall element so that the interior of the brake force booster is separated pressure-tightly from the atmosphere.
Thus, according to the present invention, the reinforcing element independently ensures the necessary sealing without requiring a separate structural element or sealing element.